As was mentioned in the comments to my entry on a refrigerant Monday, what we use has changed quite a bit over the years. If you don’t know how a fridge or AC works (they’re the exact same thing), here’s what happens: know how evaporation something makes things cooler (e.g., sweat?). Condensing something makes things hotter by the same principle. Refrigeration involves evaporating something and using the cold for what you want, then moving the vapor somewhere and compressing it (turning it into hot liquid) and dumping that heat somewhere else. Then you evaporate it again and get some more of that sweet cold stuff. And on and on it goes.
Then, we know something about a good refrigerant. It should evaporate easily, but absorb a lot of heat as it evaporates, so it cools well. There are also some ancillary concerns. It should dissolve oil, because the compressor is a motor, and it needs oil. Finally it shouldn’t be that toxic or reactive. Sulfur dioxide, an old-timey refrigerant, absorbs a lot of heat in evaporation and dissolves oil well, but it’s toxic and (somewhat) reactive. 70-80 years ago, SO2 was used in one of the earliest electric refrigerators.
It’s not used today because of toxicity concerns, but as was mentioned in the comments, home refrigerators are a lot different than car A/C – that charge of refrigerant usually doesn’t leak out.